Mono-oscillator u. h. f. transmitterreceiver



1965 TAKESHI KAWAHASHI 3,202,917

MONO-OSCILLATOR U.H.F. TRANSMITTER-RECEIVER Filed Dec. 11, 1962 62 F/9am p (F -29dbm) (POdbm) Ft -/7dbm 22 m) m/vs- M ff d z/ w/rrm ccz AFCAMP.

NA PM 75 T KAwAHAsm- T- KuRoD Atlorney United States Patent 33452317MGNQ-SStIlLLATQR UK-LEE. RANSMETTIER- Talieshi Kawahashi and TalraiiKuroda, Toltyo, .lapan,

assignors to Nippon Electric (Iorapany, Limited, Tokyo,

Japan, a corporation of .lapan Filed Dec. 11, E62, Ser. No. 243,33Claims priority, application Japan, Jan. 13, 1962, 37/1,8tl9 6 Claims.(Cl. 32520) This invention relates to a transmitter-receiver forfrequencies above 1,000 mc., and more particularly to an ultrashort waveor UHF. or S.H.F. transmitter-receiver of the heterodyne type in which aportion of the trans mitter power is used as the local oscillation powerfor the receiver.

Because U.H.F. transmitter-receivers of the above type are of simpleconstruction, requiring only one microwave tube, they have been widelyadopted. Their simplicity, however, is only relative, and conventionaltransmitter-receivers of this type still need at least two directionalcouplers, two dummy loads, and two microwave detectors; one providedwith a conversional self-check circuit requires four directionalcouplers, three dummy loads, and three microwave detectors; and one withthe transmitter A.F.C. requires four directional couplers, four dummyloads, and four microwave detectors.

Hence one object of the invention is to provide a more simplified UHF.transmitter-receiver, which may operate with only one directionalcoupler and without any dummy loads.

Another object of this invention is to provide a U.H.F.transmitter-receiver which has a reduced number of microwave detectors,but comparable reliability.

A further object of this invention is to provide a UHF.transmitter-receiver of simplified circuitry with a conversionalself-check circuit.

A still further object of this invention is to provide a UHF.transmitter-receiver in which the local oscillation frequency filter,normally used for deriving a portion of the transmitter power for thereceiver local oscillator function, serves also as a standard cavity forthe automatic frequency control of the transmitting frequency, and inwhich the microwave detector normally used for the frequency conversionof the received signal also serves as a detector for an A.F.C. signal aswell as a detector for monitoring the transmitting power.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings in which:

FIGS. 1(a) and 1(b) illustrate schematically and symbolically a typicaldirectional coupler used in a UHF. transmitter-receiver.

FIG. 2 shows a conventional U.H.F. transmitter-receiver.

FIG. 3 illustrates a UHF. transmitter-receiver according to theinvention.

In order to lay a proper foundation for an explanation of the invention,a directional coupler, typical of that generally used in U.H.F.transmitter-receivers, will first be described with reference to FIGS.1(a) and 1(1)). The coupler comprises a first waveguide forming firstand second arms 11 and 12, and a second waveguide forming third andfourth arms 13 and 14. The waveguides are mutually perpendicular and areintegrally disposed with a common wall portion containing couplingwindows 15 and 16 in the first and the third quadrants as visualizedwith respect to the axes of the waveguides.

Although most of the electromagnetic wave entering the directionalcoupler through the first arm 11 is emitted from arm 12, a portion seeksarm 13 via the coupling window 35. If the electromagnetic power enteringthe first arm 11 is P and the power transferred to the third arm 13 is POCZP11/P13 where a is the degree of coupling of the directional coupler.A very small portion of the power flows from arm 11 to the fourth arm14. If the power transmitted to the fourth arm 14 is P where 1; is thedirectivity of the directional coupler. The attenuation which theelectromagnetic wave undergoes while being transferred from arm 11 toarm 12 is determined by the coupling degree (which is approximatelyequal to the directivity).

Referring now to FIG. 2, the conventional U.H.F. transmitter-receivershown therein comprises a transmitter circuit 21, which in turncomprises a microwave oscillator having a klystron or other microwavevacuum tube, for generating a carrier wave of frequenty f which is soarranged that the carrier wave may be either directly or indirectly (viaa video frequency amplifier contained therein) modulated by the inputsignal supplied to terminal 22. The transmitter output power thusobtained is applied, via four directional couplers 23, 24, 2:5, and 2%and an isolator 27 (for preventing the deterioration in the modulationcharacteristics of the microwave tube), to antenna 30. This antenna iscapable of transmitting and concurrently receiving electric waves indifierent planes of polarization. The incoming wave of frequency 7",. isapplied through a fifth directional coupler 31 and a receiving band-passfilter 32, for suppressing the image frequency, to a receiving crystaldetector 33 which acts as a frequency converter. The etector is alsofed, through a filter 34 tuned to the local oscillation frequency f(which is equal to the transmitting carrier rrequency f with a portionof the transmitter output which appears through the first directionalcoupler 23 at its third arm 13'. The intermediate-frequency signal ofthe frequency iftfr| f1 which is thus obtained at the output side of thecrystal detector 33 is amplified, amplitude-limited, demodulated, andamplified in the well known manner in a receiver circuit 35. Theresultant signal is available at output terminal 36. It is to be notedthat where the local oscillation frequency h or, in this case, thetransmitting carrier frequency is greater than the receiver carrierfreuency f of the incoming electric wave, then fr t f1 and the imagefrequency is ft'ifi r+ 1 A portion of the transmitter output separatedat the second directional coupler Z4 is sent through a detector d1 to ameter 42 where the transmitter output is monitored with respect to itsoutput level. A further portion of the transmitter output obtained atthe third directional coupler 25 is delivered through a standard cavity44, tuned precisely to the transmitting carrier frequency f to anautomatic frequency control signal detector 45 which, after detection,produces at its output a signal which is amplified at amplifier 46 andthen fed to the transmitter portion 21 to control the oscillationfrequency of the microwave oscillator to ensure its coincidence with thetransmitting carrier frequency f The transmitter-receiver furthercomprises a conversional self-check circuit, which almost all of thetransmitter-receivers of this type include, in order to make possible anoperational check without an incoming signal. This circuit consists ofthe fourth directional coupler 23, a converted check signal oscillator48 whose oscillation frequency is approximately equal to theintermediate frequency f a crystal detector 49 which serves as afrequency converter to mix the output of the oscillator 48 with thederived portion of the transmitter output of frequency f and a fifthdirectional coupler 31 for transferring to the band pass or imagesuppression filter 32 the converted signal containing frequencies of, asthe case may be, 7, and f +2f or f, and f -Zf When the converted checksignal oscillator 48 is set into operation, only the receiver carrierfrequency f, is obtained on the output side of the image suppressionfilter 32. It is therefore possible even without an'incoming wave tocheck whether or not the transmitter-receiver 20 is in normal operation.Those arms of the directional couplers from which no power is derivedare terminated with dummy loads 51, 52, 53, and 54 in order to suppressany possible reflection.

Having laid the groundwork, the transmitter-receiver of the inventionwill now be described with reference to FIG. 3. In the followingdescription it will be understood that similarly labelled blocks andcircuit elements are similar in construction to the conventionaltransmitter-receiver shown in FIG. 2.

The most pertinent distinctions between the two circuits will first beenumerated. The receiving crystal detector 33 serves both as thetransmitter output monitoring detector 41 (in FIG. 2) and the automaticfrequency control signal detector 45 (in FIG. 2), While the localoscillation frequency filter 34 acts additionally as the automaticfrequency control cavity 44. The second, third, fourth, and fifthdirectional couplers 24, 25, 28, and '31 and the dummy loads 51-54 inthe conventional transmitter-receiver are dispensed with. Instead of thedummy load 51 connected to the first directional coupler 23, the fourtharm 14', of this coupler is connected serially to a variable orsemi-fixed attenuator 62, a bandrejection filter 63 (for rejecting thatfrequency band encompassing either the sum of, or difference between thecarrier frequency f of the incoming wave and twice the intermediatefrequency f, of the transmitter-receiver, which corresponds to the imagefrequency of the incoming wave) a crystal detector 64, and a meter 65(for checking the existence of an oscillation) in parallel with aconverted check signal oscillator 48. Furthermore, an automaticfrequency control amplifier 63 is disposed between the output of thereceiving crystal detector 33 and the microwave oscillator of thetransmitter circuit 21.

During normal operation of the transmitter-receiver, a part of thetransmitter output of frequency 73,, derived at the directional coupler23, is applied through the local oscillation frequency filter 34, tunedto the local oscillation frequency (equal to the transmitter carrierfrequency f to the receiving crystal detector 33 together with theincoming wave of frequency f Here it is frequency-converted to an outputof intermediate frequency f,. Even when there is no incoming wave, thetransmitter carrier frequency f, is supplied through the localoscillation frequency filter 34 to the receiving crystal detector 33where it is rectified and applied to the meter 61 for monitoring thetransmitter output and carrier frequency. In other words, the receivingcrystal detector 33 serves additionally as a detector for monitoring thetransmitter output and as a detector for monitoring the transmittercarrier frequency.

If the oscillation frequency of the microwave oscillator in thetransmitter portion 21 either shifts from, or is being adjusted to thedesired carrier frequency f because of either a malfunction or tubereplacement, the

portion of the oscillation derived at the directional coupler 23 isreflected by the local oscillation frequency filter 34, because of thefrequency shift, and accordingly cannot reach the receiving crystaldetector 33. Consequently, it is impossible merely with the meter 61,for monitoring the oscillation output and frequency, to judge whetherthe oscillation frequency has shifted or is not being generated at allbecause of an inadequacy, for example, in the voltages applied to thetube. It is to be noted that the local oscillation power necessary forthe receiving crystal detector 33 is generally of the order of l raw. (0dbm). It follows, therefore, that if the output of the transmitterportion 21 is mw. (20 dbm) and the transmission loss of the localoscillation frequency filter 3 is 3 db at the carrier frequency f thecoupling degree of the directional coupler 23 should be 17 db. In thisconnection, it should also be noted that the transmission loss of thedirectional coupler 23 is less than 0.1 db for a signal which goesthrough the aligned arms. Also if the directivity of the directionalcoupler is 20 db, only a small portion of the signal, about l7 dbm,emerges from the fourth arm 14'. If the oscillation frequency of themicrowave oscillator is not the desired one, the 3-dbm power derived atthe third arm 13 is reflected at the filter 3 again passing through thedirectional coupler 23, this time with minimal loss, and reaches therejection filter 63. So long as the oscillation frequency of the signalapplied to the rejection filter 63 is not approximately equal to theimage frequency, it passes through filter 63 and is rectified at thechecking crystal detector 64, appearing at the meter 65 for checking theexistence of an oscillation. Thus, it is possible with thetransmitter-receiver of the invention to easily judge whether themicrowave oscillator is producing an oscillation having a frequencyother than the prescribed one or is not generating any oscillation atall. It will, therefore, be appreciated that the checking crystaldetector 64 assumes the function of detector of the oscillator output incases of adjustment and/0r malfunction of the microwave oscillator.

Turning now to the conversional self-check feature of the invention, itwill be recalled that in the case where the output frequency of thetransmitter portion 21 is normal and equal to the resonance frequency fof the local oscillation frequency filter 34, only a very small portion(in the numerical example given above, 17 dbm) of the transmitter outputis derived from the fourth arm 14' of the directional coupler 23. If theattenuation of the variable or semi-fixed attenuator 62 is 2 db, thepower of the transmitter carrier frequency i applied to the checkingcrystal detector a4 is 19 dbm. The oscillation ouput whose frequency isnearly the intermediate frequency f if produced by the converted checksignal oscillator 43 while there is no incoming electric wave, is alsoapplied to the checking crystal detector 64, which then mixes the powersto produce a frequency-converted output of frequencies fl-f, and fH-fi.If the conversion loss of the checking crystal detector 64 is 10 db, thepower of each such converted output is ---29 dbm. Inasmuch as therejection filter 63 rejects an oscillation whose frequency is about theimage frequency, the converted check signal I that passes through thevariable or semi-fixed attenuator 62 towards the directional coupler 23,and reaches the local oscillation frequency filter 34, is approximatelyequal in frequency to the receiver carrier frequency f and in power to31 dbm. The transmission loss L of the local oscillation frequencyfilter 34, for the converted check signal whose frequency is equal tothe receiver carrier frequency f is -[Q (ftfr) Jt] which for a filterquality factor Q of 2,000, a transmitter carrier frequency f of 10,000mc., and an intermediate frequency 7, of 70 me. is:

The power of the converted check signal having passed through the localoscillation frequency filter 34 is, therefore, -60 dbm. Although thelocal oscillation power, whose frequency is equal to the transmittercarrier frequency f cannot pass through the image suppression filter 32,the converted check signal whose frequency is equal to the receivercarrier frequency f, can. The converted check signal applied to thereceiving crystal detector 33 is, therefore, a half of -60 dbm, or -63dbm, which is sufficient for the conversional self-check.

Since in the transmitter-receiver of the invention a, portion of thetransmitter output, branched at the directional coupler 23, goes throughthe local oscillation frequency filter 34 and is rectified by thereceiving crystal detector 33, if either the transmitting carrierfrequency f, or the resonance frequency h of the local oscillationfrequency filter 34 is slightly modulated with a specific frequency(such as 50 c./s.) which does not affect the quality of thetransmission, a component of the specific frequency can be detected atthe receiving crystal detector 33. It is, therefore, possible tocontrol, by the automatic frequency control signal obtained byamplifying the detected component at the automatic frequency controlamplifier 68, the oscillation frequency of the microwave oscillatorcontained in the transmitter portion 21 so that it may be exactly equalto the desired transmitter carrier frequency f In this case, thereceiving crystal detector 33 serves three functions: frequencyconversion of the received carrier, detection of the transmitter outputfor monitoring, and detection of the automatic frequency control signal.

As has been described, the conventional U.H.F. transmitter-receiver 20shown in FIG. 2 has five directional couplers, four dummy loads, andfour microwave detectors, while in the transmitter-receiver 60 of theinvention, the numbers of such components are l, 0, and 2, respectively,and the circuitry is greatly simplified. The transmitter-receiver 60 ofthe invention, therefore, not only has comparable performance to theconventional transmitfer-receiver 20, but also is very simple andeconomical. Microwave detectors are very apt to deteriorate, and theirreduction from four to only two means the elimination of approximately50% of one of the main causes of frequency troubles, and an increasedreliability. Furthermore, it will be appreciated that while inconventional transmitterreceivers, having both a frequency filter forthe receiver local oscillator function and a standard cavity for theautomatic frequency control of the microwave oscillator, the provisionof temperature compensation means is essential for maintaining theresonance frequencies precisely equal; the invention, containing as itdoes, only one local oscillation frequency filter for both functions,has no such requirement.

While the principles of the invention have so far been explained inconjunction with specific circuitry disposed in a prescribed manner, itis to be clearly understood that where necessary specific functions andtheir inherent circuitry may be eliminated. Moreover, the specificelements involved have a wide range of equivalents in the art, and thesemay be easily substituted for practical or specific reasons. Likewise,certain elements such as amplifiers, attenuators, etc. may be addedwhere necessary to boost or limit signals as is well known.

The description has been made only by way of example and not as alimitation to the scope of our invention as set forth in the objectsthereof and in the accompanying claims.

What is claimed is:

1. A simplified U.H.F. transmitter-receiver in which antenna meansradiate a first modulated carrier signal and receive a different secondmodulated carrier signal, comprising: a four arm directional coupler fortranferring signals, without substantial attenuation between the firstand second arms and between the third and fourth arms thereof, and fortransferring a first portion of signals entering said first arm to saidthird arm and for transferring a second portion, smaller than said firstportion of signals, entering said first arm to said fourth arm; atransmitter circuit for generating said first modulated carrier signalconnected to supply said first modulated carrier signals to said firstarm; means for supplying the first modulated carrier signal appearing atsaid second arm to said antenna means for radiation therefrom; a localoscillator frequency filter having a resonant frequency corresponding tothe carrier frequency contained in said first modulated carrier signal,connected to said third arm for deriving from said first signal portionsupplied to said third arm a local oscillator power signal; frequencyconversion means connected to receive both said second modulated carriersignal from said antenna means and said local oscillator power signalfrom said filter for deriving a modulated intermediate frequency signaltherefrom; detector-monitor means connected to the fourth arm of saidcoupler for detecting and monitoring said second signal portion and thesignals reflected by said filter when the carrier signal contained inthe first modulated carrier signal differs from said resonant frequency;and a receiver circuit connected to said frequency conversion means fordemodulating said modulated intermediate frequency signal.

2. A simplified U.H.F. transmitter-receiver as set forth in claim 1wherein said detector-monitor means comprises: detector means, includinga crystal diode, for detecting the carrier frequency contained in saidfirst modulated carrier signal; a rejection filter connected between thefourth coupler arm and one side of said crystal diode for rejecting theimage frequency of said first modulated carrier signal with respect tosaid resonant frequency; and LF. signal oscillator, for generatingselfcheck oscillations which have a frequency approximately equal tosaid modulated LP. output of said frequency conversion means, said IF.signal oscillator being connected to supply said self-check oscillationsto the other side of said crystal diode, said crystal diode furtherfunctioning as a frequency converter for deriving a converted outputsignal from said second signal portion supplied thereto and saidself-check oscillations, at a frequency substantially equal to thecarrier frequency contained in said second modulated carrier signal,said converted signal being applied to said frequency converter throughsaid local oscillator frequency filter.

3. A simplified U.H.F. transmitter-receiver as set forth in claim 1,wherein the transmitter circuit includes: means for generating andmodulating a first carrier signal with a first modulating signal therebyto provide a modulated carrier signal, and means for superimposing asecond automatic frequency control modulating signal, having a frequencylower than that of the first modulating signal, on the thus modulatedcarrier signal, the frequency of said second signal being selected toprevent deterioration of the quality of transmission; and wherein saidlocal oscillator frequency filter output power signal includescomponents of both said first and second modulating signals; and whereinmeans are provided and connected to supply a component of the modulatedI.F. signal output of said frequency conversion means, to saidtransmitter circuit for automatically controlling the frequency of saidfirst carrier signal.

4. A simplified UHF. transmitter-receiver as set forth in claim 3,wherein the frequency conversion means comprises: a crystal diode whichoperates simultaneously to: not only mix the local oscillator signalwith the second modulated carrier signal to derive said modulated I.F.signal but also to detect and monitor the first mod ulating carriersignal along with the automatic frequency control signals contained inthe thus mixed signals.

5. A simplified UHF. transmitter-receiver as set forth in claim 1wherein said local oscillator frequency filter includes means forsuperimposing a predetermined automatic frequency control modulatingsignal on said local oscillation power signal, said predetermined signalhaving a frequency which is lower than that of the modnlating signalcontained in said first modulated carrier signal, and which is selectedto prevent deterioration of the quality of reception; and wherein meansare provided and connected to supply a component of the modulated I.F.signal output of said frequency conversion means to said transmittercircuit for automatically controlling the carrier frequency contained insaid first modulated carrier signal.

6. A simplified U.H.F. transmitter-receiver as set forth in claim 5wherein the frequency conversion means includes a crystal diode whichfunctions simultaneously not only to mix the local oscillator signalwith said second modulated carrier signal thereby to derive saidmodulated I.-F. signal but also to detect and monitor the ReferencesCited by the Examiner UNITED STATES PATENTS 2,549,131 4/51 Rideout333-40 2,972,047 2/61 Werner et a1. 325-65 3,095,561 6/63 Hubka 325-20FOREIGN PATENTS 732,798 6/55 Great Britain.

DAVID G. REDINBAUGH, Primary Examiner.

1. A SIMPLIFIED U.H.F. TRANSMITTER-RECEIVER IN WHICH ANTENNA MEANSRADIATE A FIRST MODULATED CARRIER SIGNAL AND RECEIVE A DIFFERENT SECONDMODULATED CARRIER SIGNAL, COMPRISING: A FOUR ARM DIRECTIONAL COUPLER FORTRANFERRING SIGNALS, WITHOUT SUBSTANTIAL ATTENUATION BETWEEN THE FIRSTAND SECOND ARMS AND BETWEEN THE THIRD AND FOURTH ARMS THEREOF, AND FORTRANSFERRING A FIRST PORTION OF SIGNALS ENTERING SAID FIRST ARM TO SAIDTHIRD ARM AND FOR TRANSFERRING A SECOND PORTION, SMALLER THAN FIRSTPORTION OF SIGNALS, ENTERING SAID FIRST ARM TO SAID FOURTH ARM; ATRANSMITTER CIRCUIT FOR GENERATING SAID FIRST MODULATED CARRIER SIGNALCONNECTED TO SUPPLY SAID FIRST MODULATED CARRIER SIGNALS TO SAID FIRSTARM; MEANS FOR SUPPLYING THE FIRST MODULATED CARRIER SIGNAL APPEARING ATSAID SECOND ARM TO SAID ANTENNA MEANS FOR RADIATION THEREFROM; A LOCALOSCILLATOR FREQUENCY FILTER HAVING A RESONANT FREQUENCY CORRESPONDING TOTHE CARRIER FREQUENCY CONTAINED IN SAID FIRST MODULATED CARRIER SIGNAL,CONNECTED TO SAID THIRD ARM FOR DERIVING FROM SAID FIRST SIGNAL PORTIONSUPPLIED TO SAID THIRD ARM A LOCAL